The present invention relates to a hollow blow-molded container of a biaxially oriented saturated polyester resin or polyethelane terephthalate.
Saturated polyester resin has a wide range of applications as the material of containers such as bottles and the like, because it has excellent physical properties such as gas barrier characteristics and so forth.
A conventional bottle-shaped container of the biaxially oriented saturated polyester resin can be strengthened by the biaxial orientation, can save the quantity of the material by the reduction in the thickness of the container due to the biaxial orientation, does not permit the escape of detrimental substance such as solvent or the like from the container, and does not produce toxic gas when it is incinerated after its disposal. Such bottle-shaped containers are formed, due to the convenience of molding, thin at only the neck section and thick at the shoulder, body and bottom sections according to the biaxial orientation. During biaxial orientation blow molding, the thermal deformation temperature is extremely low. When high temperature liquid is, for example, filled in the container for heat-sterilization, the container is thermally shrunken making it impossible to fill the container accurately. Therefore, it is necessary to be subject the container to heat treatment simultaneously with or after its formation so as to enhance the thermal deformation temperature of the biaxially oriented sections of the container. It is also necessary to carry out the heat treatment to prevent a deterioration of the dimensional accuracy caused by high temperature, to prevent the occurrence of chatter, and to improve the caping accuracy by increasing the surface hardness, so as to strengthen the thick neck section of the container which is not biaxially oriented. Because the neck section of the conventional container is not biaxially oriented during blow molding, the resultant container has unstable physical properties and is susceptible to thermal deformation. However, containers, such as bottle-shaped containers, maybe required to be very tightly sealed because of the contents to be contained therein. Therefore, the neck section or end of such container is usually sealed or caulked by either a crown cap or a cap placed thereon with interposition of a packing. However, if the neck section is deformed by an external factor such as heat, the aforementioned sealing effect of the sealing means is diminished.
The conventional container of the polyethylene terephthalate resin is normally heat treated, after it is blow-molded by so-called thermal setting at a temperature exceeding the softening point of the polyethylene terephthalate resin so as to improve the thermal resistance thereof. Although the container body is subject to small thermal deformation, the neck section of the container will not be affected even by a small deformation due to the reasons described above.
The polyethylene terephthalate resin has another important feature in its transparency. The physical properties and qualtities of the contents sometimes deteriorate due to external light, depending on their properties and hence the container may need to impart resistance against external light.